Antenna input circuit for radio receivers



Nov. 7, 1950 s. TISDALE, sR

ANTENNA INPUT CIRCUIT FOR RADID RECEIVERS Filed June 29, 1945 Patented Nov. 7, 1950 UNITED STATES PATENT OFFICE' ANTENNA INPUT CIRCUIT FOR RADIO RECEIVERS This invention appertains to improvements in radio receiving circuits generally, and has among its several objects and advantages to so modify certain A.-C. and D.-C. radio circuits, particularly those which are battery operated, that received signals will be tremendously amplified and reproduced in a correspondingly increased volume, without distortion and with an appreciable economy in current consumption and, consequently, with a like saving in operating expense.

Another object of the invention has to do with the provision of methods and means for effecting increase in signal strength at both the input and output sides of radio receiving circuits for operation on broadcast wave lengths, as well as those designed for operation on short and television wave lengths, such increase in signal strength and output volume being accompanied with a substantial noise elimination.

Generally, the invention, in its simplest form, consists in imposing plate current from the output tube of a radio receiver on the grid of the R. F. amplifying tube, after the latter has been grounded through the loud-speaker voice coil, or through a coil in series with, or in inductive relation to, the loud-speaker voice coil, i. e., an anti-hum or hum bucking coil. With this circuit arrangement, the output signal strength has been found to increase to an extent that the loud-speaker ordinarily furnished with a receiver will operate at its normal volume with a greatly reduced current consumption, or a much more powerful loud-speaker can be substituted for signal reproduction with an equal, or slightly less, normal current consumption, without signal distortion. In a battery receiver, by actual test, B current for normal operation was found to be reducible by substantially one-half and A current by one-third, ,with the receiver equipped with the improved circuit arrangements disclosed herein, this saving in current consumption, and consequently in expense of operation, being accompanied with an increase in signal volume, necessitating a reduction in the current supply, or the employment of a more powerful loud-speaker.

With the foregoing and other objects and advantages in view, the invention resides in the certain new and useful combination of circuits and instrumentalities, as will be hereinafter more fully described, set forth in the appended claim, and illustrated in the accompanying drawing, i which:

The figure is a diagram of a nine tube, battery operated, receiver circuit, incorporating the mod- 1 Claim. (Cl. 250-20) ifying circuits, in accordance with the invention.

In carrying out the objects and purposes of the invention, the first effect of signal volume increase is obtained by grounding the coil of a tuned input circuit through the voice coil of the loud-speaker, or through an anti-hum, i. e., hum bucking, coil that is in inductive relation, or in series, with the voice coil. With these added circuit connections, any positive current. such as the plate current, may then be connected to the bottom of the coil through an electrolytic or other suitable condenser, or even a proper resistor.

Also, the positive current so employed may thereafter be connected to the C current anywhere in the circuit, especially, however, to the tubes before the R. F. current goes to the detector tube. While it is appreciated that these circuit changes impose a positive charge on the grid of the I. F. tube, immediately followin the transformer secondary, in addition to the negative charge that is normally impressed thereon, the operation of the circuit has proven to be successful in meeting the demand of the invention in actual practice. The second effect of obtaining a marked signal volume increase, i. e., amplification, is to be accomplished by giving the usual aerial-ground system a loop antenna effect, to which end, with an aerial wire of from forty to two hundred and fifty feet length, its input end, beyond its connection with the primary of the inductive couple, will be tapped into the secondary of the latter at its center; it being understood that the secondary may be grounded at any one of several points, for instance, to the antenna primary direct, or otherwise.

Referring to the drawing the invention is incorporated in a receiving circuit of a design found in commercial receivers, such as illustrated by, but not necessarily limited to, that of a Fall 1933 SeriesSears, Roebuck and Company Receiver, and the first of the modifying circuits, as it is exemplified therein, has for its main purpose to charge the grid of a tube, that immediately follows the inductance coil l2 of a tuned input circuit, and this is accomplished by extending a lead I 3 between one end of the antihum coil [4 and the bottom of the coil l2, and a second lead I 5 between the other end of the antihum coil 14 and the ground IS. The condenser ll, that is connected between the bottom of the coil I2 and the ground 16, has a value of .1 mfd. and it may be retained in the circuit, or omitted therefrom, depending upon which procedure affjords the better results. If left in the circuit,

3 the lead l5 will be connected between the condenser I! and the ground l6, as shown.

The second method and means for increasing the output of this standard receiver circuit, with the usual aerial-ground system employed in connection therewith, the aerial 2| being connected to the ground 23 through the primary coil 22, of the inductive couple, a lead 24 is extended between the aerial, immediately adjacent its point of connection with the primary coil 22, and is tapped in at the center of the secondary coil 25 which is in connection with the firstof the 951 tubes at the grid thereof.

and output strength and volume being particularly advantageousfor betterment 'in tonal reproduction; in the elimination of interference;

and for the increasing the range of signal reception. Greatly increased efficiency in operation will also be realized by employing these modifying circuits in connection withfrequency modulation and television circuits, as well as with submarine listening devices in time of war.

Having thus fully described my invention, it is to be understood that variations of and changes in the disclosed receiver'modifying circuits, which By means of this aerial tap from the secondary'coil 25, a loop will, in like manner, accomplish the objects and 'its other1.end:- grounded, a secondary inductance arranged adjacent to andelectromagnetically related with said primary inductance and forming a part of a tank circuit for controlling the grid of a radio tube, an elongated electrical conductor :lengths,'the powerful increases in signal input having one end connected to the antenna side of said primary inductance and its other end connected to the electrical mid-point of said secondary inductance, the connection of said conductor to said inductances providing a loop antenna efiect to augment the signal received by said antenna and fedito the grid of the radio tube.

LEO SINGLETON TISDALE, sR.

REFERENCES CITED "The following references are of record in the file of this-patent:

UNITED STATES PATENTS 

